1. Field of the Invention
The present invention relates to an electro luminescence display device, and more particularly to a fabricating apparatus and method of fabricating an electro luminescence display device that is adaptive for preventing organic EL material from flowing over adjacent pixels.
2. Discussion of the Related Art
Recently, there have been developed various flat panel displays having reduced weight and bulk, which overcomes a major disadvantage of a cathode ray tube CRT display. Such flat panel displays include a liquid crystal display LCD, a field emission display FED, a plasma display panel PDP, and electro luminescence EL display device. There is active research to increase the display quality and the screen size of the flat panel displays.
Among these, the structure and fabricating process of the PDP is relatively simple, thus the PDP is most advantageous to be made light in weight and large in size. However, the light emission efficiency and brightness of PDPs is low and their power dissipation is high. Compared to PDPs, it is difficult to make an LCD, in which a thin film transistor TFT is used as a switching device, large in size because of the associated semiconductor process. But, because LCDs are mainly used as display devices for notebook computers, the demand for them has increased. However, the LCD has a disadvantage that the power dissipation is high because the LCD requires a backlight unit. Further, the LCD has a characteristic that there is high light loss caused by optical devices such as a polarizing filter, a prism sheet, and a diffusion panel, etc. Moreover, the viewing angle of LCDs is narrow.
As compared with this, the EL display device is generally classified into an inorganic EL and an organic EL in accordance with the material of a light-emission layer. The EL display device being a self-luminous device has an advantage that its response speed is fast, its light-emission efficiency and brightness are high, and it has wide viewing angle.
The organic EL display device, as illustrated in FIG. 1, has an anode electrode 20 formed with a transparent electrode pattern on a substrate 2 and includes a hole injection layer 22, a light emission layer 24, an electron injection layer 26, and a cathode 28. The cathode electrode 28 is formed on the electron injection layer 26 and is a metal electrode.
If a drive voltage is applied to the anode electrode 20 and the cathode electrode 28, holes in the hole injection layer 22 and electrons in the electron injection layer 26 each progress toward the light emission layer 24 to excite a fluorescent material within the light emission layer 24. In this way, a picture or an image is displayed with visible light generated from the light emission layer 24.
In the organic EL display device, a small-molecule organic EL material is patterned by a vacuum deposition and a high polymer organic EL material is patterned by a coating method using an inkjet spray head or a printing system. Among the methods of fabrication, a fabricating apparatus of the high polymer organic EL will be explained in conjunction with FIG. 2.
Referring to FIG. 2, the fabricating apparatus of the high polymer organic EL according to the related art includes a supply roller 8 on which an EL material is spread, a print roller 4 to which a resin plate 6 for transferring the EL material spread on the surface of the supply roller 8 is attached, and a substrate 2 loaded under the print roller 4.
Each of red R, green G and blue B EL materials is dropped on the supply roller 8 from a dispenser 10 installed above the supply roller 8. The supply roller 8 is configured to be able to rotate in contact with the resin plate 6 attached to the print roller 4, and acts to spread the EL material dispensed onto it from the dispenser 10 onto the resin plate 6. A blade 16 or a roller is provided close to the surface of the supply roller 8 for the EL material applied to the resin plate 6 to be spread uniformly.
The print roller 4 causes the EL material from the supply roller 8 to be spread on a concave-convex pattern 12 of the resin plate 6 by rotational motion. Further, the print roller 4 causes the concave-convex pattern 12 of the resin plate 6, on which the EL material is spread, to be in contact with the substrate 2 by rotational motion, thereby forming the EL pattern on the substrate 2.
In the resin plate 6, there is formed a concave-convex pattern 12 that has the same shape as the pixel formed on the substrate 2 and has a designated width PW. The concave-convex pattern 12, as illustrated in FIGS. 3 and 4, is projected in a stripe shape with a designated gap therebetween. On the surface of the concave-convex pattern 12, there are formed a plurality of hemispherical shape grooves 30, as illustrated in FIG. 4. The concave-convex pattern 12 is contacted with the supply roller 8 on which the EL material is spread, so the EL material is uniformly spread on the concave-convex pattern 12 with a designated thickness to be transferred onto the substrate 2.
Referring again to FIG. 2, a print table 1 having the substrate 2, which is to be printed, placed is loaded by a loading device (not shown) below the print roller 4. Herein, the substrate 2 can have an electrode pattern and various material layers formed thereon for an EL display device configuration.
To describe the operation of the fabricating apparatus of the high polymer organic EL display device of the related art, the loading device (not shown) loads the substrate 2 that is placed on the print table 1. If the substrate 2 is loaded, the EL material is applied from the dispenser 10 and spread on the surface of the supply roller 8. The spread EL material is placed in the concave-convex pattern 12 of the resin plate 6 as the print roller 4 rotates. The EL material placed in the concave-convex pattern 12 is fired to form the EL pattern on the substrate 2 after being dropped on the corresponding substrate 2. After forming the EL pattern of a specific color, the same method is used to form EL patterns of other colors.
In the method of forming the EL pattern on the substrate 2 using the print roller 4, the spread of the organic EL material is accelerated right after printing as the wetting and leveling characteristics of the organic EL material are greater. As a result, the organic EL material formed on the substrate 2 is over-spread to the adjacent pixels to deteriorate color purity. In order to solve such a problem, as illustrated in FIG. 5, barrier ribs 18 are formed to reduce the spread of the organic EL material over the adjacent pixels.
However, when the organic EL material spread on the concave-convex pattern, which has a width of about 90% or more with respect to the pitch P2 of one pixel, is transferred to the substrate 2, the organic EL material 17, as illustrated in FIGS. 5 and 6, flows over the adjacent pixels to deteriorate the color purity because the gap between the barrier ribs 18 and both ends of the concave-convex pattern 12 is narrow and there is the organic EL material 17 therebetween.